Protective helmets having energy absorbing liners

ABSTRACT

In one embodiment, a protective helmet includes an outer shell and an inner liner provided within the outer shell, the liner comprising an energy absorber including a first layer, an opposed second layer, and a plurality of energy absorbing columns provided between the layers, wherein the columns include relatively long columns that are attached to both the first and second layers and relatively short columns that are attached to only one of the first and second layers.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to co-pending U.S. ProvisionalApplication Ser. No. 62/078,007, filed Nov. 11, 2014, which is herebyincorporated by reference herein in its entirety.

BACKGROUND

Sports concussion and traumatic brain injury have become importantissues in both the athletic and medical communities. As an example, inrecent years there has been much attention focused on the mild traumaticbrain injuries (concussions) sustained by professional and amateurfootball players, as well as the long-term effects of such injuries. Itis currently believed that repeated brain injuries such as concussionsmay lead to diseases later in life, such as depression, chronictraumatic encephalophathy (CTE), and amyotrophic lateral sclerosis(ALS).

Protective headgear, such as helmets, is used in many sports to reducethe likelihood of brain injury. Current helmet certification standardsare based on testing parameters that were developed in the 1960s, whichfocus on the attenuation of linear impact and prevention of skullfracture. An example of a linear impact is a football player taking adirect hit to his helmet from a direction normal to the center of hishelmet or head. Although the focus of headgear design has always been onattenuating such linear impacts, multiple lines of research in bothanimal models and biomechanics suggest that both linear impact androtational acceleration play important roles in the pathophysiology ofbrain injury. Although nearly every head impact has both a linearcomponent and a rotational component, rotational acceleration isgreatest when a tangential blow is sustained. In some cases, therotational acceleration from such blows can be substantial. Forinstance, a football player's facemask can act like a lever arm whenimpacted from the side, and can therefore apply large torsional forcesto the head, which can easily result in brain trauma.

Although the conventional wisdom is that the components of modernprotective headgear that are designed to attenuate linear impactinherently attenuate rotational acceleration, the reality is that suchcomponents are not designed for that purpose and therefore do arelatively poor job of attenuating rotational acceleration. It thereforecan be appreciated that it would be desirable to have means forattenuating not only linear impacts to but also rotational accelerationsof the head, so as to reduce the likelihood of brain injury.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood with reference to thefollowing figures. Matching reference numerals designate correspondingparts throughout the figures, which are not necessarily drawn to scale.

FIG. 1 is a cross-sectional side view of an embodiment of a protectivehelmet.

FIG. 2A is a front view of an embodiment of an energy absorber that canbe used in the helmet of FIG. 1.

FIG. 2B is a side view of the energy absorber of FIG. 2A.

FIG. 3 is a partial detail view of an energy absorbing column of theenergy absorber of FIG. 2.

FIG. 4 is a side view of a further embodiment of an energy absorber thatcan be used in the helmet of FIG. 1.

FIG. 5 is a side view of a compressed energy absorber illustratingbending and buckling of its energy absorbing columns.

FIG. 6A is a bottom view of a protective helmet of the type shown inFIG. 1 immediately prior to impact from another helmet.

FIG. 6B is a bottom view of the protective helmet of FIG. 6A during animpact from another helmet.

FIG. 7 is a side view of a further embodiment of an energy absorber thatcan be used in the helmet of FIG. 1.

FIG. 8A is a cross-sectional side view of a protective helmetincorporating an energy absorbing outer shell immediately prior to animpact.

FIG. 8B is a cross-sectional side view of the protective helmet of FIG.8B during the impact.

FIG. 9 is a rear perspective view of a first embodiment of a passivehelmet tether system.

FIG. 10 is a rear perspective view of a second embodiment of a passivehelmet tether system.

FIG. 11 is a rear perspective view of a third embodiment of a passivehelmet tether system.

FIG. 12 is a rear perspective view of a first embodiment of an activehelmet tether system.

FIG. 13 is a rear perspective view of a second embodiment of an activehelmet tether system.

DETAILED DESCRIPTION

As described above, current protective headgear is primarily designed toattenuate linear impact. However, it has been determined that bothlinear impact and rotational acceleration from torsional forcescontribute to brain injury, such as concussion. Disclosed herein areenergy absorbing systems that comprise means for absorbing energy fromimpacts to a protective helmet that minimize both translational androtational accelerations experienced by the head of the helmet wearer.In some embodiments, these means comprise an inner liner that includesenergy absorbing columns that are designed bend and buckle to attenuateboth translational and rotational accelerations. In some embodiments,the means comprise energy absorbing outer shell that locally deformsupon hard impacts to absorb energy. In some embodiments, the meanscomprise an energy absorbing tether system that limits linear movementand rotation of the helmet upon hard impact. These various means can beused independently of each other or in conjunction with each other toprotect the helmet wearer.

In the following disclosure, various specific embodiments are described.It is to be understood that those embodiments are exampleimplementations of the disclosed inventions and that alternativeembodiments are possible. All such embodiments are intended to fallwithin the scope of this disclosure.

Described below are energy absorbing systems that can be incorporatedinto protective helmets that not only address linear forces but alsotangential forces that cause the highest shear strains on the brain andthe brain stem. By optimizing protection from both linear impacts androtational acceleration, the transmission of shear force to the brainfrom head impacts can be reduced and so can the incidence of braininjury, such as concussion.

In some embodiments, a protective helmet can be provided with an energyabsorbing inner liner that utilizes energy absorbing columns havingvarious lengths and/or cross-sectional dimensions that are sandwichedbetween two elastomeric layers. The use of columns of varying lengthsand/or cross-section dimensions enables protection against impacts overa range of energy levels. When columns of different lengths are used,low-energy impacts will activate only the tallest columns, which areconnected to both layers, resulting in low translational accelerations.Higher energy impacts, however, will also activate shorter columns,which are connected to only one layer to prevent bottoming out andunacceptably high translational accelerations. The liner can be designedto provide optimal stiffness by tuning the distribution of columns tocontrol the peak accelerations applied to the wearer's head duringimpact.

As disclosed herein, the inner liner uses controlled buckling andbending of the columns to mitigate both linear and rotationalaccelerations experienced by the wearer's head. Traditional columnbuckling is a velocity-dependent process that produces high initialforces that drop very low as the column deforms. This fundamentalbehavior must be overcome if columns are to become an efficient energyabsorber for use in protective helmets and other protective equipment.One important advantage of precise column buckling that makes itattractive for use as a helmet liner is the directionality of itsresistance forces during oblique impacts that apply rotational momentsto the helmet. During this type of impact, the top of the column pushesthe helmet in the direction of the applied moment while pushing theplayer's head in the opposite direction. An advance of the disclosedliners is that linear impact dissipation can be optimized withoutadversely affecting the rotational behavior of the columns.

A column buckles when the eccentricity, or misalignment, over its lengthproduces a bending moment in the center of the column that overcomes itsbending stiffness. Hence, dynamic buckling utilizes forces from axialloading to push the middle of the column laterally. Unless themisalignment is very large, these lateral forces are small relative tothe mass of the column. As a result, the column produces a largeinertial impulse while dynamic buckling is initiated. This type ofimpulse can produce dangerous acceleration forces on the player's head.In some embodiments, the disclosed inner liner overcomes this problemusing multiple features. First, the columns of the inner liner can bemade of an elastomeric material that provides some level of axialcompression during the period in which buckling is initiated tocompensate for the magnitude of the inertial spike.

Second, the columns can be eccentric relative to the layers betweenwhich they lie to reduce the load required to initiate column buckling.These eccentricities take the form of a misalignment of the column endsfrom the normal direction of the layers so that the columns will have amoment applied upon the onset of loading. This misalignment also resultsin additional stroke because it can cause the column halves to foldbeside themselves as they collapse rather than stacking on top ofthemselves. Furthermore, the curvature of the inner liner due to thecurved nature of the helmet results in further eccentricity in thecolumns because it is likely that only a small portion of the activatedcolumns will be normal to the impact direction, thus any inertial forcescoming from these columns would be small in comparison to the overallforces generated by the sum of activated columns.

Third, as mentioned above, the column lengths can be varied. Varyingcolumn lengths accomplishes two goals. Firstly, it spreads out theinertial impulse to eliminate the high inertial spike during the earlystages of impact. Secondly, it enables the liner stiffness to beincreased with higher deflections.

FIG. 1 illustrates an example embodiment of a protective helmet 10 thatis designed to attenuate both linear impact and rotationalaccelerations. The helmet 10 shown in FIG. 1 is generally configured asan American football helmet. Although that particular configuration isshown in the figure and other figures of this disclosure, it is to beunderstood that a football helmet is shown for purposes of example onlyand is merely representational of an example protective helmet.Therefore, the helmet need not be limited to use in football. Othersports applications include baseball and softball batting helmets,lacrosse helmets, hockey helmets, ski helmets, bicycling and motorcyclehelmets, and racecar helmets. Furthermore, the helmet need not even beused in sports. For example, the helmet could be designed as aconstruction or military helmet. It is also noted that the principlesdescribed herein can be extended to protective equipment other thanhelmets. For example, features described below can be incorporated intoprotective pads or armor, such as shoulder pads, hip pads, thigh guards,shin guards, cleats, and other protective equipment in which energyabsorption could be used to protect the wearer.

With continued reference to FIG. 1, the helmet 10 generally includes anouter shell 12 and an inner liner 14. In the illustrated embodiment, theshell 12 is shaped and configured to surround the wearer's head with theexception of the face. Accordingly, the shell 12, when worn, extendsfrom a point near the base of the wearer's skull to a point near thewearer's brow, and extends from a point near the rear of one side of thewearer's jaw to a point near the rear of the other side of the wearer'sjaw. In some embodiments, the shell 12 is unitarily formed from agenerally rigid material, such as a polymer or metal material. Examplematerials are described below in relation to FIGS. 9A and 9B.

Irrespective of the material used to construct the shell 12, the shellincludes an outer surface 16 and an inner surface 18. In someembodiments, the shell 12 can further include one or more ear openings20 that extend through the shell from the outer surface 16 to the innersurface 18. The ear openings 20 are provided on each side of the shell12 in a position in which they align with the wearer's ears when thehelmet 10 is donned. Notably, the shell 12 can include other openingsthat serve one or more purposes, such as providing airflow to thewearer's head.

As is further shown in FIG. 1, a facemask 22 can be secured to the frontof the helmet 10 to protect the face of the wearer. In some embodiments,the facemask 22 can comprise one or more rod-like segments that togetherform a protective lattice or screen. When used, the facemask 22 can, forexample, be attached to the helmet 10 at points that align with theforehead and jaw of the wearer when the helmet is worn. The facemask 22can be attached to the helmet 10 using screws (not shown) that threadinto the shell 12 or into fastening elements (not shown) that areattached to the helmet. Although a particular facemask configuration isshown in the figures, alternative configurations are possible. Moreover,the facemask 22 can be replaced with a face shield or other protectiveelement, if desired.

The inner liner 14 generally comprises one or more pads that sit betweenthe shell 12 and the wearer's head when the helmet 10 is worn. In someembodiments, each of the pads is removable from the helmet. Forinstance, the pads can be configured to releasably attach to the insidesurface 18 of the helmet shell 16 with snap, T-nut, or hook-and-loopfasteners. In the illustrated embodiment, the pads include a top pad 24,multiple lateral pads 26, 28, and 30, a front pad 32, a rear pad 34, andjaw pads 36. The top pad 24 is adapted to protect the top of thewearer's head. In the illustrated embodiment, the top pad 24 iselongated in a direction that extends along the sagittal plane of thewearer so as to extend from a rear top portion of the head to a fronttop portion of the head. The top pad 24 is further curved to generallyfollow the curvature of the wearer's head. Accordingly, the top pad 24forms a concave inner surface that is adapted to contact the wearer'shead.

The lateral pads 26-30 are adapted to protect the sides of the wearer'shead. The lateral pads 26-30 extend from the edges of the wearer's faceto points behind (and above) the user's ears. Like the top pad 24, thelateral pads 26-30 are curved to follow the curvature of the shell 12and the wearer's head. Accordingly, the lateral pads 26-30 form concaveinner surfaces that are adapted to contact the wearer's head.

The front pad 32 is positioned within the outer shell 12 so as toprotect the forehead of the wearer. Like the other pads, the front pad32 is curved to follow the curvature of the wearer's head. The forwardpads 30 therefore form concave inner surfaces that are adapted tocontact the wearer.

The rear pad 34 is adapted to protect the rear of the wearer's head. Therear pad 28 is also curved to follow the curvature of the wearer's headand forms a concave inner surface that is adapted to contact thewearer's head.

The jaw pads 36 are adapted to protect the jaw of the wearer. As withthe other pads, the jaw pad 36 can curved to follow the curvature of thewearer's head and forms a concave inner surface that is adapted tocontact the wearer's head.

Several or all of the above-described pads can be of similarconstruction. In some embodiments, each of the pads comprise an outerenergy absorber 40 that is adapted to absorb translational androtational energy from helmet impacts and an inner cushion 42 that isadapted to provide comfort to the wearer's head. The energy absorbers 40releasably attach to the inner surface 18 of the shell 12. Details aboutthe construction of the energy absorbers 40 are provided below inrelation to FIGS. 2-8. It suffices to say at this point, however, thatthe energy absorbers 40 include energy absorbing columns 44 thatdissipate translational and rotational accelerations.

The inner cushions 42 of the pads contact or are at least adjacent tothe wearer's head and/or face when the helmet 10 is donned. The cushions42 can have any construction that is comfortable for the wearer. In someembodiments, the cushions 42 are foam cushions. In other embodiments,the cushions 42 are air bladder cushions.

FIGS. 2A and 2B illustrate an example energy absorber 50 that can beused in a pad that forms part of a helmet liner, such as the inner liner14 shown in FIG. 1. As shown in FIGS. 2A and 2B, the energy absorber 50generally comprises a first or inner layer 52, an opposed second orouter layer 54, and a plurality of energy absorbing columns 56 that areprovided between the layers, which can bend and buckle to absorb energy.As illustrated in the figures, the inner and outer layers 52, 54comprise thin, generally planar members that are curved to conform tothe curvature of the human head and the outer shell 12. In someembodiments, the layers 52, 54 have similar curvatures. The inner layer52 comprises an inner surface 58 that faces the outer layer 54 and anouter surface 60 that faces the wearer's head and provides a surface towhich an inner cushion 42 can be attached. The outer layer 52 comprisesan inner surface 62 that faces the inner layer 52 and an outer layer 64that can be attached to the inner surface 18 of the outer shell 12.

The energy absorbing columns 56 can comprise elongated cylindricalmembers that are substantially perpendicular to the inner and outerlayers 52, 54. As is apparent in FIGS. 2A and 2B, the columns 56 canhave various lengths or heights. Relatively long columns 66 connect theinner and outer layers 52, 54. Such columns 66 are attached at aproximal end (nearest the wearer's head) to the inner layer 52 and areattached at a distal end (nearest the shell 12) to the outer layer 54.Shorter columns 68 are only attached to one of the layers 52, 54. In theillustrated embodiment, the proximal ends of the shorter columns 68 areattached to the inner layer 52 while the distal ends of those columnsare free ends. In addition to the lengths, the cross-sectionaldimensions of the columns 56 can be varied.

In some embodiments, the energy absorber 50 can comprise columns ofseveral different lengths. For example, the energy absorber 50 couldincorporate columns 56 of 2, 3, 4, 5, or more different lengths, inwhich case the energy absorber provides multiple stages of energydissipation. In such cases, relative mild impacts may only affect thelongest columns 56 (i.e., the first stage of the energy absorber 50)while stronger impacts may affect columns of shorter lengths (i.e.,other stages of the energy absorber). This multi-stage approach providesincreased stiffness as the deflection of the energy absorber 50increases, as well as reduction in the inertial spike that comes priorto the onset of buckling in the columns 56.

An important measure of energy absorber efficiency is the achievableabsorber deflection divided by its original length. All multi-impactenergy absorbers have a maximum useable deflection beyond which thestiffness becomes excessive. This difference is normally referred to asthe stack-up distance. In some embodiments, the columns 56 are arrangedwithin the energy absorber 50 in a manner that minimizes interactionbetween adjacent columns to minimize the possibility of the columnsstacking on top of one another as the energy absorber compresses.

The thicknesses of the inner and outer layers 52, 54, the lengths andcross-sectional dimensions of the columns 56, and the ratio of columnsattached to both layers versus attached to only one layer can betailored to achieve a desired load capacity for the energy absorber 50and the pad in which it will be used. Thicker layers 52, 54 willincrease the load capacity of the columns 56 because of the stiffenedend conditions, thereby enabling the use of thinner columns. However,thicker layers 52, 54 will also increase the overall mass of the innerliner 14 because the layers represent the highest volume of material inthe system while also reducing the useable stroke. Thus, it is importantto optimize the energy absorbers 50 to provide the desired outcome ateach location within the helmet 10, taking into account factors such asavailable stroke, coverage area in the impact location, frequency ofimpact in the protected location, and overall liner mass. For instance,the front pad 32 (FIG. 1) may have larger diameter columns and a higherratio of attached columns than other pads in the liner 14 to increasethe pad stiffness due to the inherent weakness in the outer shell atthat location and the increased need for protection in the frontalregion due to the increased likelihood of impacts in that location.

In some embodiments, the outer layer 54 has a thickness of approximately0.5 to 3 mm and may contain holes for fasteners or ventilation. In someembodiments, the inner layer 52 has a thickness of approximately 0.5 to2.5 mm. In some embodiments, the energy absorbing columns 56 that areattached to both the inner and outer layers 52, 54 have lengths ofapproximately 18 to 65 mm and cross-sectional dimensions (e.g.,diameters) of approximately 3 to 7 mm, while the columns that areattached to only one of the layers have lengths of approximately 8 to 55mm and cross-sectional dimensions (e.g., diameters) of approximately 2to 6 mm. In some embodiments, the fraction of columns 56 that areconnected to both layers 52, 54 is approximately 15 to 40%, but can beincreased to as much as 100% if the pad will undergo consistent loadingand does not need to provide protection against a variety of impactconditions. While the columns 56 are illustrated in FIGS. 2A and 2B ashaving constant cross-sectional dimensions along their lengths, it isnoted that these dimensions can vary along the lengths of the columns.For example, one or more columns 56 can have a larger cross-section atits base than at other points along its length.

In some embodiments, the columns 56 can be slightly eccentric to reducethe magnitude of the inertial spike that occurs upon impact. Thiseccentricity can come in the form of an angling of the columns 56 fromthe direction normal to the inner surface of the inner and/or outerlayers 52, 54. FIG. 3 illustrates an example of this form ofeccentricity. As shown in this figure, a column 56 is offset from thenormal direction of the inner surface 58 of the inner liner 52 by anangle θ, which, for example, can be an acute angle up to approximately15 degrees. Other possible forms of eccentricities include a predefinedcurve or kink manufactured into the columns. FIG. 4 illustrates anexample of this. In this figure, an energy absorber 70 having an innerlayer 72, and outer layer 74, and a plurality energy absorbing columns76. Some of the columns 78 comprise a medial kink 80 that facilitatesbuckling.

Although the energy absorbing columns 56 have been described ascomprising cylindrical members, which typically comprise circularcross-sections, it is noted that other cross-sectional geometries arepossible. For example, the columns 56 can have an elliptical, polygonal,or other non-uniform cross-section. In addition, the columns 56 can havea twisted configuration in which the cross-section changes along thelength of the columns. For example, if the column 56 had an ellipticalcross-section, the orientation of the ellipse can rotate as the lengthof the column is traversed to form a twisted shape. Such a shape canforce the columns 56 to twist while buckling, which both increases theenergy dissipation rate in the later stages of collapse and forces thetop half of the column to land beside the bottom half, which reduces thestack-up distance and maximizes available compression in the energyabsorber.

Each of the inner liner 52, outer liner 54, and the energy absorbingcolumns 56 can be made of an elastomeric material. In some embodiments,these components are made of a thermoplastic elastomer (TPE), such asthermoplastic polyurethane (TPU). BASF Elastollan 1260D U is onecommercial example of a TPU. Other suitable TPEs include copolyamides(TPAs), copolyesters (TPCs), polyolefin elastomers (TPOs), andpolystyrene thermoplastic elastomers (TPSs).

TPU may be preferable for construction of the energy absorbers for avariety of reasons. This material can be made to be soft enough toprovide consistent initiation of the buckling process, has a rapidrelaxation time to assure high rates of energy dissipation, and hasproven to be both durable and tolerant of large temperature variations.Both the viscoelastic nature of TPU and the sensitivity of columnbuckling to impact speed enable the energy absorbing columns to absorbgreater amounts of energy as impact speed increases. This is importantfor helmets that must attenuate high speed impacts and simultaneouslyprovide optimum protection of helmet wearers who experience largenumbers of low speed impacts. Furthermore, TPU is a low cost, versatile,and commercially available material. It offers a long list ofperformance characteristics that are desirable in an environmentinvolving energy management, such as athletic equipment and militaryapplications. For instance, all grades of unreinforced TPU have highelasticity with elongation to break values of 300 to 1000%, tensilestrength to yield of 10 to 45 MPa, hardness values of 52 to 98 on theShore A scale and 22 to 95 on the Shore D scale, and material densitiesin the range of 1.05 to 1.53 g/cc.

TPU also has a low glass transition temperature of −69 to −17° C.,meaning that it will retain its elastic properties over the a broadrange of temperatures, such as that in which sports are played. Inaddition, TPU provides excellent abrasion resistance, impact strength,weather resistance, and antimicrobial properties. Additionally, TPU canbe modified to suit a particular application by adding fillers,colorants, or stabilizers. One desirable performance characteristic isthat TPU can be optimized to achieve effective damping with optimalrebound speed (e.g. short relaxation time). Finally, TPU providesfabrication flexibility, can be injection molded, and can be bonded orwelded though a variety of processes.

One potential problem associated with varying column length is thepossibility that shorter columns will slide, resulting in a bending modeof failure rather than buckling. The bending failure mode greatlyreduces energy dissipation rates. To combat this issue, a texture can beadded to the inner surfaces of the inner and outer layers as well as theouter surfaces of the columns. Such a texture is schematicallyillustrated in FIG. 3 as texture 82 and can cause the columns to lock inplace once contact is made with other columns and/or the inner and/orouter layers. In some embodiments, the texture 82 can comprise a roughsurface that is formed on the layers/columns during energy absorberfabrication (e.g., injection molding). In other embodiments, thistexture 82 can comprise a geometric (e.g., metal) mesh that isintegrated into the surfaces during fabrication (e.g., injectionmolding).

In some embodiments, the energy absorbers can be manufactured in twoparts. The first part can comprise the outer layer and all the necessaryfeatures for attaching the energy absorber to the outer shell 12, whilethe second part can comprise the inner layer and the columns that areconnected thereto. The two parts can be produced through injectionmolding or another commercial manufacturing process. Once formed, thetwo parts can be bonded together through use of welding or an adhesive.Alternatively, the layers and columns could each be manufactured asseparate parts. In such a case, the columns can comprise notches attheir ends that enable them to be snapped into place into pre-formedholes in the inner and outer layers. The columns could then be bonded tothe layers through welding or adhesion.

As discussed above, the energy absorbers are designed to deform uponimpact to dissipate energy. FIG. 5 illustrates such deformation. Asshown in this figure, an energy absorber 90 comprises an inner layer 92,an outer layer 94, and a plurality of energy absorbing columns 96. Theouter layer 94 has been pushed in toward the inner layer 92 because ofan external (downward) force and, as a result, the columns 96 of theenergy absorber 90 have bent and/or buckled under this force, therebydissipating energy.

FIGS. 6A and 6B illustrate operation of the energy absorbers whenincorporated into a protective helmet 100. As is apparent in thisfigures, the helmet 100 includes an inner liner 102 comprising multiplepads 104 having energy absorbing columns 106. FIG. 6A shows the helmet100 prior to impact. In this state, the helmet 100 is centered on thewearer's head. FIG. 6B shows the helmet 100 upon receiving a tangentialimpact from another helmet 110. As can be appreciated from this figure,the energy absorbing columns 106 near the point of impact have deformedto absorb the energy of the impact. In addition, the helmet 100 hasrotated relative to the wearer's head to dissipate the rotational forceimparted by the helmet 110 instead of delivering it directly to thewearer's head. In such a case, the wearer's head can remain relativelystationary, at least in terms of rotation, while the helmet 100 rotates.Once the force is removed, however, the energy absorbing columns 106 canreturn the helmet 100 to its original orientation on the head.

It is noted that the energy absorbers can comprise other componentsbesides columns between their inner and outer layers. For example, FIG.7 illustrates an energy absorber 120 comprising an inner layer 122, anouter layer 124, and a plurality of energy absorbing columns 126.Provided between the inner and outer layers 122, 124 in a free spacebetween the columns 126 is a supplemental energy absorbing member 128.The member 128 can comprise a foam element or an air bladder elementthat provides increased energy dissipation where needed, such as nearthe front of a helmet. In the illustrated embodiment, the member 128 isgenerally elliptical with its long axis extending along the normaldirections of the inner and outer layers 122, 124.

The basic premise of impact energy management is to optimize energyabsorption in each component of a system. So, while the inner linersdescribed above can be used to absorb energy, other components of thehelmet can likewise be designed to absorb energy. Once such component isthe outer shell of the helmet.

The shell material in most commercial football helmets is made ofpolycarbonate (PC) alloys or acrylonitrile butadiene styrene (ABS)plastic in thicknesses ranging from 3 to 4 mm. While these materialshave high impact resistance, they exhibit a highly elastic response toimpacts. Therefore, the energy absorbed by the shell material isminimal. Greater energy could be absorbed, however, if the shell wasmade of a deformable, energy absorbing material.

With reference back to FIG. 1, the outer shell 12 of the protectivehelmet 10 can be made of such a material. In some embodiments, the shell12 is made of a polyethylene (PE) composition, such as high densitypolyethylene (HDPE). HDPE is a class of thermoplastic polymers thatincorporate long chains of polyethylene mers with molecular weights inthe range of approximately 100,000 to 3,000,000. HDPE is a suitablereplacement for the elastic PC or ABS materials used in current footballhelmets, whether or not the helmets include an inner liner of the naturedescribed above.

A protective helmet must meet the requirements under its workingconditions. Football helmets are required to absorb energy, resistgouging, fatigue, and creep, operate in extreme ambient temperatures(−12° C. and 52° C.), accept paint and dyes, and be readilymanufacturable. HDPE is a low-cost, versatile, and commerciallyavailable material. It offers a long list of performance characteristicsthat are desirable in an environment involving energy management, suchas athletic equipment and military applications. Specific parameters ofa suitable HDPE composition include the following:

-   -   Tensile Strength to Yield: ˜25-31 MPa    -   Rockwell Hardness (Shore D): ˜55-75    -   Elongation to Break: ˜900-1300%    -   Flexural Modulus: ˜1000-1500 MPa    -   Melt Flow Index: ˜5 to 8 g/10 minutes

Additionally, HDPE offers a lower density (0.95 g/cm³) when compared toconventional PC (1.2 g/cm³) or ABS (1.05 g/cm³) formulations. A lowerdensity can be advantageous by providing lower weight to the wearer or athicker geometry for the same weight. In some embodiments, the shell hasa thickness of approximately 2.4 to 4 mm. HDPE also offers a low glasstransition temperature of −70° C. to −80° C.

It is important to note that energy absorbing outer shells can be toosoft. If the local deformation of the shell is too high, impactinghelmets can become entangled or interlocked such that high forces can begenerated parallel to the surface of the shell. This type of loadingproduces high rotational accelerations in the helmet. High rotationalaccelerations are also produced when hard accessories, such asfasteners, gouge into the surface of the shell material. Typical HDPE'smay not offer sufficient slip (low friction) or abrasion resistance tocounter mechanical interlock as described above. The polyethylene of theHPDE can be compounded with one or more additives to combat theseissues. Such additives can include a processing stabilizer that protectsthe polymer at high temperatures, a heat stabilizer that inhibitsdegradation of the end product, a slip agent that reduces frictionbetween surfaces (i.e., increases slip), and an ultraviolet stabilizerthat inhibits environmental degradation. ADDCOMP ADD-VANCE 148 and 796are two example commercial multi-functional additives that could beused. A range of approximately 1 to 8% by weight of the additives can becompounded with the PE base in the composition.

Football helmet shells are often dyed in a similar color in which theywill be painted or coated after manufacturing. The HDPE compositiondescribed herein can readily accept up to 3.5% by weight, which issuitable for the range of colors on the market. Once a HDPE helmet hasbeen manufactured, its surface energy can be increased by 2-5 dynes/cmthrough corona treatment or other processes to impart wettability, whichenables paint particles to adhere to the helmet.

FIGS. 8A and 8B illustrate the effect of constructing the outer shell 12of the protective helmet 10 out of an energy absorbing material, such asHDPE. FIG. 8A shows the helmet 10 prior to impact. FIG. 8B shows thehelmet 10 upon receiving an impact to the top of the shell 12. As can beappreciated from this figure, the shell 12 has locally deformed at thepoint of impact and thereby dissipates some of the impact force. Asbefore, the energy absorbing columns 56 have also deformed near thepoint of impact.

Another way in which energy imparted to a protective helmet can beabsorbed is tethering of the helmet. Tethering a helmet involvesattaching one or more flexible tethers between the wearer's helmet andan object securely anchored to the wearer's body. Such tethers greatlyincrease the helmet's resistance to motion by firmly securing the helmetto the wearer's upper body. If properly designed, tethers can reducepeak accelerations by as much as 80 percent by raising the effectivemass of the head and helmet from approximately 13 lbs. to over 70 lbs.

An effective helmet tether system can incorporate the followingfeatures: A) enables the head/neck complex to freely rotate andposterior flex when not being struck; B) provides resistance toacceleration when helmet is struck; C) cannot apply excessive force tohelmet; D) cannot obstruct players vision; and E) easily attaches anddetaches from the helmet.

A helmet tether system can be designed as a passive or an active system.Passive tether systems are designed to resist extreme motions, such asexcessive deflection or velocity. Active tether systems, however,incorporate sensors that sense when an impact has either begun or isabout to occur and includes actuation mechanisms that actively respondto such sensed conditions.

FIG. 9 illustrates a first embodiment of a passive helmet tether system140 that links a protective helmet 142 to an article 144 (shoulder padsin this example) worn by the helmet wearer. The system 140 includesmultiple tethers 146 that extend between the helmet 142 and the shoulderpads 144. More particularly, a first or upper end of each tether isattached to the interior or exterior of the outer shell 148 of thehelmet 142, and a second or lower end of each tether is attached to theouter shells 150 of the shoulder pads 144. In the illustratedembodiment, the lower ends of the tethers 146 are attached to andwrapped around spools 152 that are fixedly mounted to the shoulder padouter shells 150. The spools 152 are free to rotate to enablelengthening of the tether 146 to enable turning of the head until themaximum length has been reached, at which point the tether limitsfurther helmet movement. By limiting the degree to which the helmet 142can be move relative to the body, the tether system 140 limits theforces that can be transmitted to the wearer's head. In someembodiments, the tethers 146 comprise high-strength, flexible, inelasticcords. Example inelastic cord materials include steel, nylon,polypropylene, and polyethylene.

In some embodiments, the spools 152 can comprise internal torsionsprings (not shown) that take up any slack that forms in the tethers146. In other embodiments, the spools 152 can further comprise internallocking mechanisms (not shown), such as centrifugal brakes, thatautomatically lock the angular orientations of the spools, and thereforehalt lengthening of the tethers 146, upon a threshold angularacceleration being reached. The threshold angular acceleration can beone that is associated with movements of the helmet 142 that exceed thespeed with which the wearer can move his or own head, which areindicative of a helmet impact.

FIG. 10 illustrates a second embodiment of a passive helmet tethersystem 160 that links a protective helmet 162 to an article 164(shoulder pads) worn by the helmet wearer. The system 160 is similar tothe system 140 in that a first or upper end of each tether 166 isattached to the outer shell 168 of the helmet 162, and a second or lowerend of each tether is attached to the outer shells 170 of the shoulderpads 164. However, this embodiment comprises no spools. Instead, thetethers 146 comprise flexible, elastic cords that resist movement asthey are stretched. Example elastic cord materials include elastomerssuch as synthetic rubber, and TPU, and fiber-reinforced elastomers.

FIG. 11 illustrates a third embodiment of a passive helmet tether system180 that links a protective helmet 182 to an article 184 (shoulder pads)worn by the helmet wearer. This system 180 is also similar to the system140 shown in FIG. 9. Accordingly, the system 180 comprises multipletethers 186 having a first or upper end attached to the outer shell 188of the helmet 182, and a second or lower end attached to the shoulderpad outer shells 190. In this embodiment, however, an extensionmechanism 192 is provided along each tether 186. Lengths of the tethers186 are wound around an internal spool (not shown) within the extensionmechanism 192, which also includes an internal torsion spring (notshown) that takes up slack. The extension mechanism 192 can furtherinclude a locking mechanism (not shown) that automatically locks theangular orientation of the internal spool, and therefore haltslengthening of the tether 186, upon a threshold angular accelerationbeing reached.

FIG. 12 illustrates a first embodiment of an active helmet tether system200 that links a protective helmet 202 to an article 204 (shoulder pads)worn by the helmet wearer. The system 200 includes multiple tethers 206that extend between the helmet 202 and the shoulder pads 204. Moreparticularly, a first or upper end of each tether is attached to theinterior or exterior of the outer shell 208 of the helmet 202, and asecond or lower end of each tether is attached to and wrapped aroundspools 210 that are releasably mounted to the shoulder pad outer shells212. The system 200 further comprises pre-tensioned springs 214 that areattached at one end to a spool 210 and attached at the other end to theshoulder pad outer shell 212. In addition, the system 200 includes animpact sensor 216, such as an accelerometer, that is mounted to thehelmet 202 or the wearer's head. The impact sensor 216 is incommunication with a central controller 218 that is adapted to actuatethe spools 210.

During use of the system 200, the spools 210 are free to rotate toenable lengthening of the tether 206 to enable turning of the head untilan impact that exceeds a force threshold is sensed by the sensor 216.When such an impact occurs, the central controller 218 activatesactuation mechanisms (not shown) associated with each spool 210 thathalt further rotation of the spools and decouple the spools from theshoulder pads 204. When this occurs, the tethers 206 will no longerlengthen and the springs 214 will pull down on the spools 210 to removeslack from the tethers.

FIG. 13 illustrates a second embodiment of an active helmet tethersystem 220 that links a protective helmet 222 to an article 224(shoulder pads) worn by the helmet wearer. The system 220 includesmultiple inelastic tethers 226 having a first or upper end attached tothe outer shell 228 of the helmet 222, and a second or lower endattached to and wrapped around spools 230 that are fixedly mounted tothe shoulder pad outer shells 232.

The system 220 further comprises multiple sensors 234, such asaccelerometers, that are mounted at multiple points on the helmetwearer's body (multiple locations of the shoulder pads 224 in theexample of FIG. 13). The data collected by the sensors 234 can beprovided to a central controller 236 that executes a control algorithmthat determines from wearer's body posture and motion that a helmetimpact is likely to occur. In such a case, the central controller 236can activate pre-tensioning mechanisms (not shown) associated with eachspool 232 that wind the tethers 226 onto the spools 230 to prepare thehead for an impending impact. In some embodiments, the control algorithmcomprises a heuristic algorithm that adapts to the individual helmetwearer over time. In the case of a sports helmet, data from bothpractice and live game play can be used to refine the heuristicalgorithm. In some embodiments, the pre-tensioning mechanisms cancomprise electro-active materials used to form the tethers 226, such asdielectric elastomers. Signaling of such electro-active tethers could beused to induce changes in stiffness and strain.

1. A protective helmet comprising: an outer shell; and an inner linerprovided within the outer shell, the liner comprising an energy absorberincluding a first layer, an opposed second layer, and a plurality ofenergy absorbing columns provided between the layers, wherein thecolumns include relatively long columns that are attached to both thefirst and second layers and relatively short columns that are attachedto only one of the first and second layers.
 2. The helmet of claim 1,wherein the energy absorber is made of a thermoplastic elastomer.
 3. Thehelmet of claim 2, wherein the energy absorber is made of thermoplasticpolyurethane.
 4. The helmet of claim 1, wherein the energy absorbingcolumns are cylindrical.
 5. The helmet of claim 1, wherein there arethree or more different lengths of energy absorbing columns in theenergy absorber so as to provide three or more different stages ofenergy absorption.
 6. The helmet of claim 1, wherein the relatively longcolumns are approximately 18 to 65 millimeters long and approximately 3to 7 millimeters in cross-sectional dimension.
 7. The helmet of claim 1,wherein the relatively short columns are approximately 8 to 55millimeters long and approximately 2 to 6 millimeters in cross-sectionaldimension.
 8. The helmet of claim 1, wherein the energy absorbingcolumns form acute angles no greater than approximately 15 degrees withthe normal directions of the layers.
 9. The helmet of claim 1, whereinthe energy absorbing columns and at least one of the first and secondlayers have a textured surface that reduces slippage.
 10. The helmet ofclaim 1, wherein the energy absorbing columns are kinked.
 11. The helmetof claim 1, wherein the energy absorber includes a supplemental energyabsorbing member positioned between the first and second layers and in aspace formed between the energy absorbing columns.
 12. The helmet ofclaim 1, wherein the inner liner further comprises an cushion adapted tocontact a wearer's head.
 13. An inner liner for use inside an outershell of a protective helmet, the inner liner comprising: an energyabsorber including a first layer, an opposed second layer, and aplurality of energy absorbing columns provided between the layers,wherein the columns include relatively long columns that are attached toboth the first and second layers and relatively short columns that areattached to only one of the first and second layers.
 14. The liner ofclaim 13, wherein the energy absorber is made of thermoplasticpolyurethane.
 15. The liner of claim 13, wherein the energy absorbingcolumns are cylindrical.
 16. The liner of claim 13, wherein there arethree or more different lengths of energy absorbing columns in theenergy absorber so as to provide three or more different stages ofenergy absorption.
 17. The liner of claim 13, wherein the relativelylong columns are approximately 18 to 65 millimeters long andapproximately 3 to 7 millimeters in cross-sectional dimension.
 18. Theliner of claim 13, wherein the relatively short columns areapproximately 8 to 55 millimeters long and approximately 2 to 6millimeters in cross-sectional dimension.
 19. The liner of claim 13,wherein the energy absorbing columns form acute angles no greater thanapproximately 15 degrees with the normal directions of the layers. 20.The liner of claim 13, wherein the energy absorbing columns and at leastone of the first and second layers have a textured surface that reducesslippage.
 21. The liner of claim 13, wherein the energy absorbingcolumns are kinked.
 22. The liner of claim 13, wherein the energyabsorber includes a supplemental energy absorbing member positionedbetween the first and second layers and in a space formed between theenergy absorbing columns.
 23. The liner of claim 13, wherein the innerliner further comprises an cushion adapted to contact a wearer's head.